Do state any willing provider laws inhibit the ability of managed care to reduce health care costs by forcing health plans to relinquish some control over the panel of providers? Researchers developed a compendium of AWP laws, reviewing each state AWP statute and classifying it with respect to providers covered, types of managed care firms covered, dates of enactment and implementation, and the nature of the enforcement provisions. In addition, they estimated the effects of AWP laws on: 1) prescription drug prices paid by HMOs and PPOs; 2) the number of participating providers in managed care firms and on the administrative costs of expanded participation; 3) managed care firms' market penetration; and 4) on health insurance premiums. The objective of this study was to better understand the impact of AWP laws on the growing managed care industry.